Broadcast is a communication scenario or modality where a single transmitter sends independent information to multiple non-cooperating receivers. The broadcast channel was introduced by T. Cover in “Broadcast Channels”, IEEE Trans. Inform Theory, 1972, where an achievable capacity region of the degraded channel is derived by means of superposition coding. T. Cover, “An Achievable Rate Region for the Broadcast Channel,” IEEE Trans. Inform. Theory, 1975, and E. van der Meulen, “Random Coding Theorems for the General Discrete Memoryless Broadcast Channel,” IEEE Trans. Inform. Theory, 1975, disclose an inner bound for degraded discrete memoryless broadcast channels. Marton presented an inner bound of a class of nondegraded broadcast channel in “A Coding Theorem for the Discrete Memoryless Broadcast Channel,” IEEE Trans. Inform. Theory, 1979.
Recently the capacity region of multiple-input multiple-output (“MIMO”) Gaussian broadcast channel has been studied intensively due to its applicability and benefits in wireless communications applications. The sum capacity of the multi-user MIMO broadcast channel is well studied, see for example, G. Caire and S. Shamai, “On the Achievable Throughput of a Multiantenna Gaussian Broadcast Channel,” IEEE Trans. Inform. Theory, vol. 49, no. 7, pp. 1691-1706, July 2003; Wei Yu and I. M. Cioffi, “Sum Capacity of Gaussian Vector Broadcast Channels,” IEEE Trans. Inform. Theory, vol 50, no. 9, pp. 1875-1892, September 2004; and S. Vishvanath, N. Jindal and A. Goldsmith, “Duality, Achievable Rates, and Sum-Rate Capacity of Gaussian Mimo Broadcast Channels,” IEEE Trans. Inform. Theory, vol 49, no. 10, pp 2658-2668, October 2003. Dirty paper coding (“DPC”) is a key technology discussed in these papers to derive the sum capacity of the MIMO Gaussian broadcast channel.
A well-known practical DPC approach, known in the art as Tomlinson-Harashima precoding (“THP”), is described in H. Harashima and H. Miyakawa, “Matched-Transmission Technique for Channels with Intersymbol Interference,” IEEE Trans. Commun., vol. 20, pp. 774-780, August 1972; and, M. Tomlinson, “New Automatic Equaliser Employing Modulo Arithmetic,” Electronics Letters, vol. 7, pp. 138-139, March 1971. THP was originally developed for intersymbol interference (“ISI”) channels. Its simple structure makes THP a very attractive solution for DPC implementation. U. Erez, S. Shamai(Shitz), and R. Zamir. “Capacity and Lattice-Strategies for Cancelling Known Interference.” In Proceedings of ISITA 2000, Honolulu, Hi., pp. 681-684, Nov. 2000. However THP suffers a 1.53 dB capacity loss in the scalar case due to shaping, although the capacity gap can be eliminated by using vector lattice coding with much higher complexity.
Since THP is a nonlinear operation, it inevitably causes some quantization noise. The inventors herein have developed a method to reduce the effect of the quantization noise introduced by nonlinear coding. Towards this end, we observe that in some applications, the interference may be of a particular modulation structure that is known to the receiver. This is often the case, for example, in wireless applications where the interference is a known, modulated signal. For example, we disclose a method that reduces the performance loss by taking advantage of the known modulation structure information of the interference signal.